The OSI standard provides a seven-layered hierarchy between an end user and a physical device through which different systems can communicate. Each layer is responsible for different tasks, and the OSI standard specifies the interaction between layers, as well as between devices complying with the standard. The OSI standard includes a physical layer, a data link layer, a network layer, a transport layer, a session layer, a presentation layer and an application layer. The IEEE 802 standard provides a three-layered architecture for local networks that approximate the physical layer, and the data link layer of the OSI standard. The three-layered architecture in the IEEE 802 standard 200 includes a physical (PHY) layer, a media access control (MAC) layer and a logical link control (LLC) layer. The PHY layer operates as that in the OSI standard. The MAC and LLC layers share the functions of the data link layer in the OSI standard. The LLC layer places data into frames that can be communicated at the PHY layer, and the MAC layer manages communication over the data link, sending data frames and receiving acknowledgement (ACK) frames. Together the MAC and LLC layers are responsible for error checking, as well as retransmission of frames that are not received and acknowledged.
The IEEE 802.11e standard (IEEE P802.11e/D13.0 (January 2005), “Amendment: Medium Access Control (MAC) Quality of Service (QoS) Enhancements”), specifies a contention-free medium access control scheme for applications with strict delay requirements. Such a medium access control scheme is a type of time reservation scheme in which an access point (AP) allocates time periods for channel access by different stations (STAs) during a contention-free period. However, currently few manufacturers can support contention-free access control schemes in wireless devices due to implementation complexity. Most IEEE 802.11 wireless local area network (WLAN) devices can only support a contention-based medium access control scheme.
With the proliferation of high quality audio/video (A/V), an increasing number of electronics devices (e.g., consumer electronics devices) utilize high A/V information such as high definition (HD) A/V information. Conventional WLAN IEEE 802.11a/b/g and pre-N wireless devices cannot meet the real-time bandwidth requirements for such high quality A/V transmissions without delay and packet loss. For example, a HD television signal (HDTV) stream of 14 megabits per second (Mbps) over the IEEE 802.11a/g devices with 54 Mbps capacity and over pre-N devices with 108 Mbps, cannot be transmitted from a sender (i.e., source STA) to a receiver (i.e., destination STA) over a wireless channel and played back smoothly. One reason is that for the same application, uplink packets from the sender to the AP, and downlink packets from the AP to the destination, contend the wireless channel simultaneously. This increases packet collisions which causes longer delays, degrading throughout. If acknowledgement packets from the destination to the source are utilized, throughput performance is further degraded. The IEEE 802.11e standard allows a direct link (direct communication) between two STAs without an AP. However, if the two STAs are far apart (i.e., hidden nodes), proper communication between them may not be possible, or the PHY rate capacity of the direct link may be too low to support real-time requirements of HDTV transmissions.